fix: add return on empty user/pass, and do not send superfluous 200 OK

[ajcasagrande]

There was a missing return statement in the section that checks if the username or password is empty. Also, warning messages were present that would say superfluous WriteHeader for 200 OK.

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PR Checklist

Please check if your PR fulfills the following requirements:

• [X] I am not introducing a breaking change (if you are, flag in conventional commit message with BREAKING CHANGE: describing the break)
• [X] I am not introducing a new dependency (add notes below if you are)
• [N/A] I have added unit tests for the new feature or bug fix (if not, why?)
• [X] I have fully tested (add details below) this the new feature or bug fix (if not, why?)
• [N/A] I have opened a PR for the related docs change (if not, why?)

Testing Instructions

Build and run this PR using Debug Logging. Fill out credentials for user/pass for rtsp server Call Start Streaming API Expect the logs:

level=DEBUG app=device-usb-camera source=driver.go:194 msg="rtsp authentication: username or password is empty"
level=DEBUG app=device-usb-camera source=driver.go:220 msg="rtsp authentication: passwords match"

New Dependency Instructions (If applicable)

[vyshali-chitikeshi]

Validation looks good. With rtsp user name and password, streaming starts successfully and get below msgs in log level=DEBUG ts=2023-05-16T00:12:44.735054278Z app=device-usb-camera source=driver.go:194 msg="rtsp authentication: username or password is empty" level=DEBUG ts=2023-05-16T00:12:44.782961748Z app=device-usb-camera source=driver.go:220 msg="rtsp authentication: passwords match"

Without rtsp user name/password (or empty credentials), start streaming fails and get below msgs in log level=DEBUG ts=2023-05-16T00:11:16.539368151Z app=device-usb-camera source=driver.go:194 msg="rtsp authentication: username or password is empty" level=DEBUG ts=2023-05-16T00:11:16.58683335Z app=device-usb-camera source=driver.go:194 msg="rtsp authentication: username or password is empty"